INDUSTRIAL ELECTRONICS
THYRISTORS are used to categorize an entire
class of semiconductor devices. They are four
layer, pnpn devices used as electronics
switches
TYPES OF THYRISTORS:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Silicon Controlled Rectifier(SCR)
Shockley Diode
TRIAC(Triode AC)
DIAC (Diode for AC)
Silicon Controlled Switch (SCS)
Gate Turn-Off Thyristor (GTO)
Light Activated SCR (LASCR)
Silicon Unilateral Switch (SUS)
Silicon Bilateral Switch (SBS)
Silicon Controller Rectifier is a three-terminal
device used to control quite large currents to a
load. One SCR can control power up to 10
Megawatts, and a relay of SCRs have been used
to control greater than 100 Megawatts. It has a
frequency range of application of about 50KHz.
Turning ON an SCR:
1. SCR operate like two transistors.
2. The positive pulse of current at the
gate triggers an SCR.
3. The SCR can be turned on without gate
triggering by increasing VAK to VBR(F0).
This means rising of temperature of the
device makes a significant change to
the value of VAK to the breakover value.
SCR Characteristics & Ratings:
1. Forward Breakover Voltage – Voltage
at which SCR enters forward conduction
(on) region.
2. Holding Current – value of anode
current for SCR to remain in on region.
3. Gate trigger current – value of gate
current to switch SCR on.
4. Average forward current – maximum
continuous anode current that the SCR
can withstand.
5. Reverse-breakdown voltage –
maximum reverse voltage before SCR
breaks into avalanche.
Two General Methods of Turning OFF and
SCR:
1. Anode – Current Interruption
A. Series Interruption
- Using and PBNC ( Push-Button
Normally Close) switch, if
pressed, the anode current is
interrupted.
B. Shunt Interruption
- Using a PBNO (Push Button
Normally Open) switch, if
pressed the anode current is
interrupted.
2. Forced-Commutation Technique
- “Forcing” of current through an
SCR in the direction opposite to
forward conduction.
Shockley Diode is the simplest of all thyristors.
It has two terminals, labeled anode and
cathode. The construction of a four-layered
diode is the same as SCR except that it has no
gate terminal.
TRIAC stands for TRIode AC which is
fundamentally a DIAC with a gate terminal for
controlling the turn on conditions of the
bilateral device in either direction. It is
equivalent to two SCRs connected in inverseparallel. It has three-terminal namely the Main
Terminal 1 (MT1), Main Terminal 2(MT2), and
Gate.
DIAC stands for Diode for AC which is basically
a specialized diode. Its construction is basically,
two Schockley Diode joined in parallel facing
different direction. It has a typical breakover
voltage of 20V-40V.
sensitive to temperature changes, unlike SCR
which vary widely with changes in ambient
Silicon Controlled Switch (SCS) is a tetrode
thyristor, which has four electrodes. It has an
anode gate(AG) like PUT and cathode gate(KG)
like SCR. It can be trigger on either direction
but can be turn off only using a large reverse
current through the anode. The applications of
SCS largely in voltage and current sensing. SCS
has faster turn-off with pulses on either gate
but it has lower maximum current and voltage
rating than SCR.
Advantages of SCS over SCR:
1. Reduced turn-off time (1-10us)
2. Increased control and triggering
sensitivity.
3. More predictable firing situation.
Gate Turn-Off Thyristor (GTO) or sometimes
known as Gate-Controlled Switch is a power
switching device that can be turned on by a
short pulse of gate current and turned off by a
reverse gate pulse. The reverse gate amplitude
needed to turn off is nearly one-fifth as large as
its principal current. GTOs are commonly used
as counters, pulse generators, multivibrators
and voltage regulators.
Light Activated SCR (LASCR) is an SCR which
state is controlled by light. The gate may be
biased by a voltage or current slightly less than
its gate-trigger requirements, thereby varying
the amount of light necessary to trigger it.
Silicon Unilateral Switch (SUS) is firmly a trigger
or logic device. The SUS triggers within a half of
percent of its rated value despite of nominal
temperature changes which means it is not
temperature.
NOTE:
Isinama ko na po yung ibang thyristors. Hindi ko
na po nilagyan ng description since di sila
common na ginagamit mahihirapan lng aralin.
NakaBOLD na po yung important terms. Yung
sample problems po I’ll try na ituro next time
madali lang nman po baka sa library nlng.
“SABI NI LORD MAGIGING ELECTRONICS
ENGINEER KA NGAYONG 2014…. :) ”